1. Field of the Invention
The present invention relates to recording information signals, such as digital image signals, on writable recording media, such as DVDs (Digital Video Discs), while information for copy control that is able to represent at least two states, i.e., a state allowing one copy and a state prohibiting copy subsequently or absolutely, is added to the information signals.
2. Description of the Related Art
Recently, with the expanding use of digital media, such as the Internet and digital video discs, illegal copying of digital works, such as digital pictures and digital books/articles has become a problem. To cope with the problem, it is proposed to add information for copy control to the digital works and prevent illegal copying based on the added information.
It is also proposed to provide the option of not allowing copying at all, or allowing copying once but prohibiting copying from the thus-produced copy (generation-limiting copy control system). The former control is applied to, e.g., original software that is prepared by contents makers and brought into the market in the form of DVD-ROMs or the like. The latter generation-limiting copy control system is applied to, e.g., broadcast information.
In the latter generation-limiting copy control system, there are proposed a CGMS (Copy Generation Management System) and a method utilizing electronic watermark processing.
The electronic watermark processing implies a process of xe2x80x9cburyingxe2x80x9d information as noise in a portion of image data or music data which is not important from the viewpoint of human perception. Additive information buried in image data or music data by the electronic watermark processing is hard to remove. On the other hand, even after image data or music data has been subjected to a filtering process or a data compressing process, additive information buried therein can still be extracted.
In a typical copy control system utilizing the electronic watermark processing, the following four states are used to represent the copy generation and the copy limiting condition of image data or music data on which electronic watermark information is superimposed:
(1) xe2x80x9ccopy allowed free (Copy Free)xe2x80x9d,
(2) xe2x80x9cone (only one generation) copy allowed (One Copy)xe2x80x9d,
(3) xe2x80x9cmore copy prohibited (No More Copy)xe2x80x9d, and
(4) xe2x80x9ccopy absolutely prohibited (Never Copy)xe2x80x9d.
The state of (1) xe2x80x9cCopy Freexe2x80x9d represents that image data or music data can be copied freely. The state of (2) xe2x80x9cOne Copyxe2x80x9d represents that image data or music data is allowed to be copied once. The state of (3) xe2x80x9cNo More Copyxe2x80x9d represents that image data or music data has been copied from the image data or the music data in the (2) xe2x80x9cOne Copyxe2x80x9d state, and further copying thereof is prohibited. The state of (4) xe2x80x9cNever Copyxe2x80x9d represents that copying is absolutely prohibited.
If the electronic watermark information superimposed on image data or music data is in the xe2x80x9cOne Copyxe2x80x9d state, a recording apparatus adapted for the electronic watermark processing (i.e., for the copy limitation processing) determines that copy recording of the image data or the music data is allowed, and executes the recording. At this time, electronic watermark information indicating xe2x80x9cNo More Copyxe2x80x9d is superimposed on the image data or the music data being recorded. Thereafter, with the electronic watermark information superimposed on image data or music data in the xe2x80x9cNo more Copyxe2x80x9d state, a recording apparatus adapted for the electronic watermark processing prohibits further recording of the data.
A copy control method utilizing the CGMS is described below. For an analog image signal, for example, two-bit additive information for copy control is superimposed thereon in one particular horizontal zone within a vertical blanking period. Also, for a digital image signal, two-bit additive information for copy control is added to digital image data and then transmitted together therewith.
The two-bit information (hereinafter referred to as CGMS information) used in the CGMS method can have the following meanings:
(00) . . . copy allowed free,
(10) . . . one (only one generation) copy allowed, and
(11) . . . never copy (copy absolutely prohibited).
The CGMS method does not include the above-mentioned xe2x80x9cNo More Copyxe2x80x9d state.
If the CGMS information added to image information is (10), a recording apparatus adapted for the CGMS determines that copy recording of the image information is allowed, and executes the recording. At this time, the CGMS information rewritten to (11) is added to the thus-recorded image information. Thereafter, if recording of the image information having the added CGMS information of (11) is attempted, a recording apparatus adapted for the CGMS determines that copy recording of the image information is not allowed, and prohibits execution of the recording.
As described above, copy generation limiting control has been hitherto implemented by limiting recording of information for which copying is to be controlled, such as image data or music data, based on additive information for copy control. With such a conventional method, when a first copying is executed by recording apparatus adapted for the CGMS or electronic watermark processing, but a second copying is executed by recording apparatus not adapted for the CGMS or electronic watermark processing, the above-described recording limitation for the second generation copy is not implemented, and the second generation copy is generated in the same state as the first generation copy.
Such a situation will be described in more detail as to the case of copying digital image data with reference to FIG. 21.
In the example of FIG. 21, one channel of cable TV broadcasting is selected and received by a set top box 1, and digital TV broadcasting signals of a program of the selected channel are recorded on a disc recording medium 3 by a recording apparatus 2 adapted for the copy limitation processing. Then, the disc recording medium 3 is played back by a reproducing apparatus 4 adapted for the copy limitation processing, and reproduced output signals are recorded by a recording apparatus 5 not adapted for the copy limitation processing.
Assume that, in the example of FIG. 21, the program selected by the set top box 1 includes copy control information, and the information indicates that the recorded program is allowed to be copied once. In other words, the two-bit CGMS information (10) is superimposed on information of the broadcasting program when the CGMS method is used, and the electronic watermark information indicating the xe2x80x9cOne Copyxe2x80x9d state is superimposed thereon when the electronic watermark processing is used. Note that an abbreviation WM in FIG. 21 represents electronic watermark information.
The recording apparatus 2 adapted for the copy limitation processing detects the CGMS information or the electronic watermark information WM superimposed on the information of the broadcasting program, and determines the detected information. If the detected information represents xe2x80x9cOne Copyxe2x80x9d, the information of the broadcasting program is recorded on the disc recording medium 3. At the same time, the CGMS information is rewritten to (11), and the electronic watermark information WM is rewritten to xe2x80x9cNo More Copyxe2x80x9d.
The disc recording medium 3 on which the information of the broadcasting program, including the rewritten information for copy control, has been recorded (copied) is played back by the reproducing apparatus 4 adapted for the copy limitation processing. The, reproduced output signals, particularly analog output signals, from the reproducing apparatus 4 may be supplied in some cases to the recording apparatus 5 which is not adapted for the copy limitation processing, i.e., the CGMS or electronic watermark processing.
However, because the recording apparatus 5 is not adapted for the copy limitation processing, the information of the broadcasting program, on which the CGMS information or the electronic watermark information WM in the state representing exactly the same copy generation as the first generation disc recording medium 3 is superimposed, is recorded on a new recording medium 6, as shown in FIG. 21.
The illegally copied recording medium 6 can be normally played back even with reproducing apparatus not adapted for the copy limitation processing, and the reproduced information of the broadcasting program can be normally looked at and listened to by viewers. Thus, the illegally copied recording medium 6 is treated as a legally copied disc, illustrating how illicit copying cannot be effectively prevented.
In view of the state of art set forth above, an object of the present invention is to provide a method and an apparatus which can essentially disable reproduction of information signals from an illegally copied recording medium, and can prevent illicit copying effectively.
To achieve the above object, a reproducing and/or recording system is provided, in which copy generation of an information signal is controlled through the use of copy control information that is added to the information signal. The copy control information takes on at least one of three possible states, a one-copy allowed state, a more-copy prohibited state and a copy absolutely prohibited state. The system determines an initial copy control state for the signal being reproduced and determines the state of copy control information to be added to the reproduced signal based on at least the initial copy control information. During recording it may be determined that no further copy control information is to be added to the signal.